The degrees to which poor populations are spatially concentrated within metropolitan areas are influenced by two sets of forces. In this article, I refer to the first set of forces as redistributive forces, which includes intrametropolitan forces that redistribute populations among different neighborhoods. The second set of forces includes metropolitan-wide processes that alter the relative poverty composition of the overall metropolitan population. These latter processes are referred to here as compositional forces. This research investigates the degrees to which these two sets of forces impacted poverty concentration among racial and ethnic groups within Los Angeles County, CA from 1990 to 2000. Both forces generally functioned to increase poverty concentration among all groups considered, with compositional forces having the stronger effect. Evidence suggests that the residential experiences of poor whites, African Americans, and Hispanics were strongly influenced by the migratory behavior of the nonpoor in Los Angeles. The Asian population, however, exhibited some evidence of ethnic (or racial) ''self-selectivity,'' as this population exhibited less interclass segregation over time. Despite increased poverty concentration, findings demonstrate that Los Angeles became slightly less segregated by race and ethnicity during the 1990s.Over time, researchers have expressed considerable interest in the residential environments of the urban poor in the United States. In recent decades, poorer urban populations have become increasingly concentrated within neighborhoods that are segregated from those inhabited by the nonpoor. This has been particularly true in the case of the minority poor. Concern for the consequences of this spatial arrangement has increased recently as a result of a growing literature focusing on ''neighborhood effects'' (Brewster